[linux-dvb] Re: reading two elementary PIDs (Aud and Vid) atonce

[Holger Waechtler <holger@convergence.de>]

Hi Matt,

there are many things changed since your patch, could you please 
regenerate your patch using "diff -pu" so that I can see the function names?

thanks,

Holger



Matt Davis wrote:
> On Thursday 31 October 2002 04:07 pm, Mike Doyle wrote:
> 
>>Does this mean I should be trying another way of getting two Elementary
>>streams (any suggestions)?
>>
>>If not, is there a fix? Or work around?
>>
>>thanks again
>>Mike
> 
> 
> When trying to do the same thing, I found in the "old" driver that when 
> DmxDevRead was called it locked the underlying dmxdev mutex so that all other 
> reads were blocked.  A second process would grab the lock and starve the 
> first process because of the race condition set up with two processes trying 
> to read the demux device.  The way we got around it was to add a filter 
> specific mutex and to use this mutex when DmxDevRead was called, instead of 
> locking the dmxdev mutex.  This allowed multiple filters to be read at one 
> time, thereby fixing the problem.  We are in the process of converting to the 
> new drivers so I do not yet know if the same problem exists there...	
> 
> Here is the patch to the old driver if it is of any use...  hope this helps.
> 
> 
> [mdavis cvs]$ diff -ru DVB/ temp/DVB/
> diff -ru DVB/driver/dmxdev.c temp/DVB/driver/dmxdev.c
> --- DVB/driver/dmxdev.c Thu Aug  1 11:46:11 2002
> +++ temp/DVB/driver/dmxdev.c    Thu Aug 15 12:49:57 2002
> @@ -722,6 +726,7 @@
>                  return -EMFILE;
>         }
>          dmxdevfilter=&dmxdev->filter[i];
> +       sema_init(&dmxdevfilter->mutex, 1);
>         file->private_data=dmxdevfilter;
>  
>         DmxDevBufferInit(&dmxdevfilter->buffer);
> @@ -747,6 +752,11 @@
>                 up(&dmxdev->mutex);
>                 return -EINVAL;
>          }
> +       
> +       if (down_interruptible(&dmxdevfilter->mutex)) {
> +               up(&dmxdev->mutex);
> +               return -ERESTARTSYS;
> +       }
>  
>          DmxDevFilterStop(dmxdevfilter);
>         DmxDevFilterReset(dmxdevfilter);
> @@ -761,6 +771,7 @@
>         }
>         DmxDevFilterStateSet(dmxdevfilter, DMXDEV_STATE_FREE);
>         wake_up(&dmxdevfilter->buffer.queue);
> +       up(&dmxdevfilter->mutex);
>         up(&dmxdev->mutex);
>         //printk("free filters = %d\n", DmxDevFilterNum(dmxdev));
>          return 0;
> @@ -907,7 +924,7 @@
>          dmxdev_filter_t *dmxdevfilter=DmxDevFile2Filter(dmxdev, file);
>         int ret=0;
>  
> -        if (down_interruptible(&dmxdev->mutex))
> +        if (down_interruptible(&dmxdevfilter->mutex))
>                 return -ERESTARTSYS;
>  
>         if (dmxdevfilter->type==DMXDEV_TYPE_SEC)
> @@ -916,7 +933,7 @@
>                 ret=DmxDevBufferRead(&dmxdevfilter->buffer, 
>                                      file->f_flags&O_NONBLOCK, 
>                                      buf, count, ppos);
> -        up(&dmxdev->mutex);
> +        up(&dmxdevfilter->mutex);
>         return ret;
>  }
>  
> @@ -937,14 +954,26 @@
>  
>         switch (cmd) {
>         case DMX_START: 
> +               if (down_interruptible(&dmxdevfilter->mutex)) {
> +                     up(&dmxdev->mutex);
> +                     return -ERESTARTSYS;
> +               }
> +
>                 if (dmxdevfilter->state<DMXDEV_STATE_SET)
>                         ret=-EINVAL;
>                 else
>                         ret=DmxDevFilterStart(dmxdevfilter);
> +
> +               up(&dmxdevfilter->mutex);
>                 break;
>  
>         case DMX_STOP: 
> +               if (down_interruptible(&dmxdevfilter->mutex)) {
> +                     up(&dmxdev->mutex);
> +                     return -ERESTARTSYS;
> +               }
>                 ret=DmxDevFilterStop(dmxdevfilter);
> +               up(&dmxdevfilter->mutex);
>                 break;
>  
>         case DMX_SET_FILTER: 
> @@ -954,8 +983,14 @@
>                 if (copy_from_user(&params, parg, sizeof(params)))
>                         
>                         ret=-EFAULT;
> -               else
> +               else {
> +                       if (down_interruptible(&dmxdevfilter->mutex)) {
> +                               up(&dmxdev->mutex);
> +                               return -ERESTARTSYS;
> +                       }
>                         ret=DmxDevFilterSet(dmxdev, dmxdevfilter, &params);
> +                       up(&dmxdevfilter->mutex);
> +               }
>                 break;
>         }
>  
> @@ -965,13 +1000,24 @@
>                 
>                 if (copy_from_user(&params, parg, sizeof(params)))
>                         ret=-EFAULT;
> -               else
> +               else {
> +                       if (down_interruptible(&dmxdevfilter->mutex)) {
> +                             up(&dmxdev->mutex);
> +                             return -ERESTARTSYS;
> +                       }
>                         ret=DmxDevPesFilterSet(dmxdev, dmxdevfilter, &params);
> +                       up(&dmxdevfilter->mutex);
> +               }
>                 break;
>         }
>  
>         case DMX_SET_BUFFER_SIZE: 
> +               if (down_interruptible(&dmxdevfilter->mutex)) {
> +                     up(&dmxdev->mutex);
> +                     return -ERESTARTSYS;
> +               }
>                 ret=DmxDevSetBufferSize(dmxdevfilter, arg);
> +               up(&dmxdevfilter->mutex);
>                 break;
>          
>          case DMX_GET_EVENT: 
> diff -ru DVB/driver/dmxdev.h temp/DVB/driver/dmxdev.h
> --- DVB/driver/dmxdev.h Mon Oct 29 05:51:26 2001
> +++ temp/DVB/driver/dmxdev.h    Wed Aug  7 15:08:30 2002
> @@ -96,6 +96,8 @@
>          struct dmxdev_s *dev;
>          dmxdev_buffer_t buffer;
>  
> +        struct semaphore mutex;
> +
>          // only for sections
>          struct timer_list timer;
>          int todo;
> 
> 
> 
> 
> 



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